1. Field of the Invention
The present invention generally relates to a device for controlling a single-phase power conditioner for a renewable energy system and, more particularly, to a control device for a single-phase power conditioner for a renewable energy system, thereby the renewable energy system is tied with the utility system to provide electricity when the utility system functions normally, otherwise the load consumes transferred power with negligible transfer time when one of the utility system and the renewable energy system does not provide electricity. In the present invention, the power conditioner provides better efficiency and output voltage waveform.
2. Description of the Prior Art
The distributed energy system and the renewable energy system are tied in parallel with the utility power system in practical uses. However, the load requires electricity even when the renewable energy system or the utility power system is mal-functional. Therefore, power transfer is required for the load. In order to reduce the influence of power transfer upon the load, the transfer time needs to be shortened and the swing and distortion of the output voltage of the utility power system need to be minimized.
In U.S. Patent Publication No. 20050006958 filed by Dubovsky, the transfer switch is switched to the power system, which is grid-tied with the renewable energy system, when the power system operates normally. In this grid-tied mode, the load consumes power from the power system. When the power system is mal-functional, the transfer switch is switched to the renewable energy system. In this standalone mode, the renewable energy system only provides power for some key loads such as emergency lights, life support systems and precision equipments. However, during power transfer from the grid-tied mode to the standalone mode, a surge current/voltage often occurs. Moreover, it often takes a considerable period of time for detection. And a power storage system is required for transient output power compensation.
Please also refer to U.S. Patent Publication No. 20030025397 filed by Douglas Gibbons, wherein a magnetic contactor is used for power transfer. Similar to U.S. Patent Publication No. 20050006958, it takes a considerable period of time for power transfer, wherein a surge current/voltage often occurs.
Furthermore, in U.S. Pat. No. 6,304,006 filed by M. Aaron, the load is supplied with electrical power using the standalone mode and the grid-tied mode. When the backup power system or the renewable energy system stops providing electricity, the load consumes electrical power either by way of a rectifier R1 (or a controllable rectifier system) with a filter circuit (F1), a bus and a standalone inverter or from a power storage device by way of a bus and a standalone inverter. In this patented invention, the complexity increases as the number of elements and interfaces increases. Similarly, a surge current/voltage often occurs during power transfer when the power system is mal-functional.